Shortly after Donald Trump won the presidency in 2016, a debate broke out about the future of the Democratic Party: Should it work to recapture white voters who had fled and voted so overwhelmingly for Republicans? Or should Democrats continue down the path of so-called "identity politics" and double down on efforts to build a racially diverse coalition of voters?

Thanks to developments this week, we can put that choice in clearer terms: Are Democrats going to be the party of Joe Biden or Ta-Nahesi Coates?

Judging by the early returns, Bidenism has a limited future. The real question, perhaps, is whether his approach is still potent enough — and President Trump unpopular enough — that he can win the presidency in 2020?

The likely answer: no.

Let's rewind to Tuesday night. Biden, the former vice president and current Democratic presidential candidate, caught flack after he decided to profess nostalgia for the early 1970s, a time when he could work side-by-side in the Senate with notorious segregationists like Sens. James O. Eastland of Mississippi and Herman Talmadge of Georgia and still get stuff done.

"I was in a caucus with James O. Eastland. He never called me 'boy,' he always called me 'son,'" Biden said Tuesday at a New York fundraiser, adding: "You go down the list of all these guys. Well guess what? At least there was some civility."

The backlash was fierce. Even Sen. Cory Booker — the New Jersey Democrat who has tried to power his presidential campaign on good vibes and avoiding confrontation — called out Biden. "I have to tell Vice President Biden, as someone I respect, that he is wrong for using his relationships with Eastland and Talmadge as examples of how to bring our country together," Booker said.

Coates, meanwhile, isn't running for anything — he is a writer, not a politician. But his advocacy for racial justice represents an important constituency within the Democratic Party: His 2014 cover story for The Atlantic called "The Case for Reparations" stirred a dormant debate on the issue. On Wednesday, he went before a House subcommittee to make a passionate, detailed plea for the government to start work on the topic.

The question of reparations for slavery and Jim Crow, Coates said, "is one of making amends and direct redress, but it is also a question of citizenship." He added: "This body has a chance to both make good on its 2009 apology for enslavement, and reject fair-weather patriotism, to say that this nation is both its credits and debits."

Unlike Biden, Coates won plaudits for his comments from prominent Democrats and pundits. That would suggest which way the wind is blowing. But Biden may be able to overcome those headwinds, at least in the short term: He leads his rivals in the polls, is raising money at a prodigious rate, and has longstanding membership in a Democratic establishment terrified that Sen. Bernie Sanders (I-Vt,) will win the nomination and doom the party to an unending Republican campaign against socialism. And a recent poll shows that Biden, along with Sanders, is leading among young African-American voters.

Those advantages mask real weaknesses, though. Biden's unapologetic approach risks alienating African-American voters, or at least dimming their enthusiasm to get to the polls on Election Day 2020. That's a constituency that Democrats cannot afford to lose, even a little bit: In 2016, 11 percent of African-American voters who voted for Barack Obama in 2012 stayed home rather than turn out for Hillary Clinton. She lost.

The kicker: Biden also risks losing white Democratic voters who have remained with the party. New research suggests that the percentage of racially liberal white Democrats is growing rapidly — from 19 percent in 2012 to 40 percent in 2016. White Democrats "increasingly hold a perspective that acknowledges racism and discrimination as obstacles to black success," wrote Andrew Engelhardt, a postdoctoral researcher at Brown University.

That suggests the Democratic future will continue to be broadly multicultural.

What does this mean for 2020? Biden, in his efforts to reach out to Obama voters who fled to Trump, could end up inadvertently abandoning the constituencies that currently power the Democratic Party. That's politically dubious: The best candidates are able to shore up their base and reach beyond it, but adequate candidates at least accomplish the former. Trump may be unpopular with the general public, but his strength within the Republican Party gives him a fighting chance at re-election.

Right now, Democrats seem to be trying to have it both ways: The Coates agenda is front-and-center in Congress, after all, while Biden remains at the head of the party's presidential pack. But the tension can't last forever — and neither will liberal nostalgia for buddying up with segregationists. Joe Biden may or may not win the 2020 nomination, but one thing is increasingly clear: He has already lost the battle for the Democratic Party's future.